


How to Import Save Files -

by SomewhereRains



Category: Undertale (Video Game)
Genre: Aged-Up Frisk (Undertale), Bodyswap, F/M, Female Frisk (Undertale), Gender or Sex Swap, High School, Male Protagonist, Masturbation, Mind Control, Mind Manipulation, My First AO3 Post, My First Smut, Not in a physical way, Other Additional Tags to Be Added, Post-Canon, Post-Undertale Pacifist Route, Reader Is Not Frisk (Undertale), Reader-Insert, Self-Indulgent, Self-Insert, Slow To Update, Some Plot, Sorry Not Sorry, Uses Y/n, Verbal Frisk (Undertale)
Language: English
Status: In-Progress
Published: 2021-01-14
Updated: 2021-01-14
Packaged: 2021-03-18 16:28:53
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,501
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28746234
Author URL: https://archiveofourown.org/users/SomewhereRains/pseuds/SomewhereRains
Summary: You've been friends with Frisk for years, even before they'd become the monster's ambassador. Having a crush on them for years but being faced with no way to reciprocate, it drives you down a strange road of inclinations, ideals, and ideas. Your SOUL has a special power, that of coercion. Being able to not only bend the minds of others, but to transform into them as well. You end up replacing Frisk for a few days, eventually leading you into becoming her entirely.And you couldn't be happier. Maybe she isn't the only one you should experiment with...
Kudos: 4





	How to Import Save Files -

You’ve been friends with Frisk for months. Years, actually. Known for being the monster’s ambassador, she was always the talking point of the grade. Never the popular one, but people always seemed to know who she was, no matter where you’d go. Their SOUL trait was also especially rare, being determination. Since all humans had some level of determination in them, they were unique, as they had the power to control a SAVE file.

Nevertheless, you’ve known her since childhood. She’d call the both of you soul mates, considering just how many times you’ve been there for her. Whether to give advice on homework, or alleviating the weight on her shoulders, you always helped her in her time of need, even when she had to reintroduce an entire race of people back into society.

Would it be strange to say you’ve had a crush on her for years? Your gift was never all that interesting, it was always seen as one of the more vague and rare traits. ‘You’d have to be a genius to get proper use out of it,’ was a constant phrase said by your peers. That of ‘control,’ whatever that means. Each trait gave some unique special abilities, your first being the spell ‘coercion.’ 

Basically, it’d make people forget what they were saying for a few moments, and then they’d be sorta easily susceptible to suggestion. What a talent, right? But that’s where things start getting interesting.

Recently, you’ve gained the power to shapeshift yourself, as well as others. Crazy, right? Sounds too good to be true, but it’s the truth. Unfortunately, from what little you’ve tested it, it feels like you’re only able to do so for a little over an hour. But, progress has been fast, especially considering not too long ago, it only lasted twenty minutes. 

Strange, right? That’s what you thought. But hey, that’s your story. Hopefully you’ll be able to use it for something productive. It does sound pretty dangerous... 

“Y/N, wait up!” Monster Kid would shout out, a wide smile spread on his face. “Oh hey, Mk.” You respond with, as he follows in your stead. “I didn’t know you took this way to school dude, you shoulda told me; My place is just up the road!” He hurriedly sputters his words, out of breath from running up to you. “Yeah… Sorry, dude. I meet up with Frisk on the way.” Your words come out with a shrug-like gesture, unsure of what to say. After that debacle, you look around for her.

“Y/N!” Frisk yells, waving as she walks towards you and Monster Kid. “Hey, Frisk! How’ve you been?” You ask, reflecting on how she’s been hounded by legal people recently. That sort of thing apparently happened a lot with her, considering the whole ‘monster representative’ ordeal.

“I’ve been fine, if a little worn out.” She says, letting out a chuckle as she walks alongside you. Monster Kid is notably eyeing up her body; Namely her breasts, as he walks on the other side of you. It makes you uncomfortable, but despite that, your gaze follows his as they bounce. She seems out of breath, several trickles of sweat travelling down her chest. You couldn’t see any bra straps over her shoulders, so you started to wonder if she was even wearing one… You desperately wanted to know.

...But anywho. Monster Kid knows Frisk from when she first fell down Mt. Ebott, so it’s not that weird having him walk with you two. You’ve been sorta off and on friends with him, he’s a bit of a screw up, so it’s kinda difficult staying around him for too long. You turn back to Frisk.

A short sigh escapes you, as you speak up. “Yeah… but we’re getting through it. I’ll be there to talk if you need me.” After hearing your reassurance, her face shifts into a warm smile. The three of you approach the school, eventually splitting off in different directions. 

* * *

It’s finally time to start magic training, the only interesting subject of the day. Frisk is in this class with you, as well as Monster Kid. The three of you all sit and listen to the teacher prattle on for a while about the crazy power of SOULs or whatever.

“The thing about human SOULs is that, even if it isn’t necessarily one of their abilities, in states of heightened emotion or stress, they can exhibit new powers on the fly. Most traits get use of it in combat scenarios, though it can really occur whenever. The new powers that appear though, are only temporary, and must be related to whatever the human’s SOUL trait is.” The teacher babbled on, with most of the class having already stopped listening. Frisk though, was deeply entranced by this notion.

“So hypothetically speaking, if something like that happened with my determination, it could be even as powerful to do something like… be determined enough to refute death?” Frisk blathered out this line, raising her arm to speak while saying it. You perk an eyebrow at her, a bit confused as to what she meant by this... Other students did the same, the teacher, likewise. The teacher took a very long time to think their response over.

“...Potentially?” They confusedly replied, the class shifting back to ignoring the lesson in an instant. This got you thinking, and now you were actually paying attention. Thoughts started to dance in your head, slowly but surely. ‘Heightened emotion?’ That sounded… interesting. Heh, now you have an idea. This may turn out really bad, but… The risk would be worth the reward.

After class would end, you’d walk up to Frisk and greet her as she packed up her belongings. “Uh… hey! I know this is pretty sudden, but what you said in class earlier got me thinking, and I was wondering if I could try out a new spell of mine with you.”

Frisk’s expression shifted from a confused one, to an intrigued and seemingly flattered one. As the teacher and the other students would leave, Monster Kid would then stay behind, watching people leave, resting at the corner of the room, next to the door.

“Oh, I’d love to! I’ve always wanted to know more about your trait you know, considering just how fussy you are about keeping it a secret!” Frisk snickers, resting a hand on her enormous hips. “Hey… It’s just a sensitive spot, ok? Oh and uh, Mk, do you want to watch too?” You ask, meeting his eyes as he shifts his head towards you two. He always waited for everyone in class to leave before him for whatever reason, and that made him even more of a perfect candidate.

“Um, sure, heheh. What’re you two on about?” Monster Kid asks under his breath, having barely been paying attention. “I uh, well I wanna try my new spell, but I don’t have a combat oriented trait, so I was thinking of-'' You gently force out in response, then being cut off by his follow up response. “Oh, sure dude! Human traits are always super cool dude, so go for it.” ...You sigh, taking in an exasperated inhale. This should go the way you want it to. “So, ahem,” You clear your throat, before looking over to Frisk while speaking. “My spell is… Well... basically, I can transform into people.”

A wave of confusion spreads over their expressions, although after a few seconds, Frisk’s starts to shift into an excited one. “Ooh! Does that mean you could transform into like, me, or even one of the teachers?” She sounds... surprisingly okay with this. Monster Kid is reacting how you would expect, a little bit dazed even at the prospect, but Frisk is… Excited to test it out.

“Heheh, yeah… I guess I could. That’s actually… well, could I use it on you?” Was your meek reply, though she seemed pretty instantly on board. “Sure! ...Umm, do I have to do anything special?” Was her first question, then followed by a “How long can you do it for?” and a “Wait, can you use my SOUL trait too?” which was then ended with a “Ooo… We could be like twins!”

A fire practically caught in Monster Kid’s eyes at that notion. He must be so jealous of you right now. You smile, now making a flushed expression as you speak. “I’ll uh… test it now.” 

A few moments go by before your body completely erupts in light. You can slowly start to feel all your proportions change, as well as hair, clothing, and accessories. It feels like your chest had to have gained forty pounds, you almost started to fall before Frisk’s next words woke you up. “Woaaah!! We like, totally match!!” Her words startle you into standing up straight, which is then followed by your two friends eagerly eyeing up your new body.

Well… it certainly looks like they had a reason to. You could feel them dangling around, almost splatting together with every little movement… Frisk’s tits… She really wasn’t wearing a bra. It took everything out of you not to just start groping yourself in front of them. Your ass wasn’t half bad either… Even while standing still, you could tell it was immensely squishy. It felt like nothing was keeping your butt in place, from how delicately it bounced around. Moving your rear around a bit, you eventually get a feel for the bikini-esque panties that Frisk had been wearing. You almost moan as you finally get a fit for your new body. Frisk doesn’t seem to notice, but Monster Kid sure does.

They stand there speechless for a little while longer, before you speak up. “Oh… wow. Heheh, I’m surprised it worked.” You sound exactly like her. Your mannerisms, tone of speech, it’s all there, clear as day. You’ve gained her muscle memory as well, carrying around her body just like she would. You’re content with this, smiling at the both of them.

“Wow… clothes and all!” Frisk picks up with, examining every little part of you. She gets very close at times, just shy from touching you with her face. You feel a little awkward, but nevertheless, you have to keep this plan going. “Wow! We're almost exactly alike… Actually wait… Hey Monster Kid, Frisk, wanna test something out?” You speak, surprised to find yourself even naturally imitating her sentence structure; You practically have to force your old one out.

They both tilt their heads off to the side, curious of what you’re hypothesizing. “So like… I haven’t actually used this much, but I wanna see if you can tell which of us is the real one. Just from a guess!” You sound really excited and peppy, just like Frisk would be, though you try to hold back.

Both of them smile in response, Monster Kid doing a shrug-like motion. You further explain your idea, a smile forming on your face as well. “So then, Monster Kid, after a while, you turn around, and guess which one is the real Frisk!”

They both seem not that interested in the idea initially, which causes you to get flustered a little bit, but after they see you all embarrassed, they can’t themselves but agree to your idea. “Sure!”

This is perfect, now’s your chance! “Okay Mk, turn around. I’ll tell you when to turn back, okay?” You solemnly respond, turning to face Frisk with a smile as bright as hers.

She seems a little flustered by this, you and her cheeks reddening by the looks you offer each other. Right after you watch Monster Kid turn his back, you immediately take action. A piercing gaze is forced in Frisk’s direction, her eyes meeting yours. The coercion spell should work for this, it has done far more in the past…

She almost jerks back as she takes in your power, a soft, almost inaudible whine coming from her as she begins to stumble. Her body then leans up, a soft, lethargic expression on her face. You walk over to her, grasp her by the shoulder, and daintily walk her to where you once stood.

You then walk back to where Frisk was initially standing, and after a few seconds, you eagerly shout out your words. “Ok, now turn around!” Frisk straightens up a bit, but looking a little dizzy. It sorta reminds you of yourself, after not getting enough sleep at night. “...So, which one do you think is the real Frisk?” You let out, intentionally speaking in Frisk’s cute and innocent tone, all the while making careful little movements, copying her body language down to the finest detail.

Monster Kid turns his eyes to Frisk, giving a loud and exasperated expression. “Aww… come on dude, I knew you were doing those footsteps to trick me. Maybe if you’d actually stood in her place, I woulda been fooled, heh heh!” He snickers as he finishes his sentence, you giggling in response. “Aww, but he looks so cute as me, though!! I guess I do gotta get to my next class… You should probably turn back then, Y/N…” You respond in a whiny tone, Frisk’s eyes meeting yours. She seems confused, but with the spell in effect, gaps start to fill in her mind easier. “But I’m... I... yeah. I guess you’re right…” She uneasily responds, now holding her head in anguish. 

“So, see you in PE?” You say, meeting Monster Kid’s eyes. His cheeks red up as he turns to get his backpack. As he does this, you approach Frisk and raise a palm in her direction. You also give her a penetrating glare, casting both Coercion and Shapeshift at the same time. Light erupts from her, as her features start to change to those that were once yours. Her mind must feel like mush at the moment, so she should be pretty susceptible to any commands you give her. After waving to Monster Kid as he leaves the room, you lean into Frisk’s ear. “You did a good job being me, Y/N. Y/N will be a good boy and finish his next period, alright? After next period, I’d also like to meet you on the roof, okay? And um, before I forget… After I leave the room, you’ll forget we had this conversation, alright? You’ll still follow my orders though, cutie~!”

You give her the softest hug your new body can muster, proceeding to pack up her belongings with the brightest of smiles on your face. You’ve done it! Shutting the classroom door behind you, turning back to sneak glances at your new  _ plaything _ through the classroom door window.

She’s packing up your belongings, and copying what she remembers of your body language… 

How cute.

* * *

You squee quietly to yourself as you shut the door. The girl’s bathroom… Ahh this is so exciting! You hang Frisk’s backpack on the bathroom door hook, then after doing so, you proceed to examine your body more thoroughly. You should have roughly over an hour in here, so this is your time to make use of your newfound... assets. You feel for Frisk’s booty shorts; They’re of similar material to her sweater, same colors, too. Odd fashion choice, though you don’t mind.

Her midriff was quite spacious… Rather risky of her to not wear a bra with so much of her body exposed. She also wore expensive looking black leggings, that covered all the way up to the shorts. It felt rather snug, though that was partially because of how little was covering you.

You tug your shorts and leggings down first, basking in all the little tickles they make on your body while pulling them down. Your panties fell instantly, damp from your pussy’s juices. You slowly start to rest on the toilet seat, taking in the process of it.

Nnnn... It makes you moan a little. The new sensation of your fat naked ass resting out openly… It makes you feel alive. You pry at both ends of your rear, then letting them slap back together. Ahh...! Such a good girl. You can feel your butthole clench up a little in response afterwards.

Your pussy has been getting wetter and wetter ever since you first inhabited this body, your libido growing tenfold since you’d left the classroom. Considering Frisk should be in Physical Education right now, she shouldn’t be in too much trouble for… taking a little, ah... break.

You spread your legs a little, gazing down at your dripping sex. It folds together nice and cutely, the lips are also nice and fat. You place one of your hands on it. Frisk’s hands. Just touching it makes you shudder. You pause briefly, taking the moment into account. Frisk is the girl of your dreams… and you are her now. You remember the serene words you’d whispered into Frisk’s ear, legs quaking a little. Your hand reaches for your snatch almost reflexively.

You spread your legs out much wider, far enough out to see the pink parts. Once you spread them out far enough, a large amount of juice drizzles out of your pussy, and you can hear the little noises it makes when it hits the water. This only further excites you.

You reach in first with your middle finger, pulling upward around the top, slowly. The little changes in texture, the way pulses against your fingers, it’d be wrong not to call it ecstasy. Even using only one finger, your body jerks forward repeatedly in pleasure.

You add a second finger, the pointer. You scrape the outer sides of your vagina with them, tickling it and jerking forward frequently. Heehee… Mmm. Ooo! You perk up a little, tracing your fingernail around your clit. It makes you jump back a little in shock, both of your arms perching back reflexively in really a cute way. Your face turns a bright red, looking off to the side.

Now, finally, the ring finger. Even from just touching it, your legs twitch. You have to reach away to stop the rush… You giggle a little, now feeling new sensations tickling your breasts. Looking down, you see that her sweater has latched onto your tits from all the sweat that’s accumulated.

Mmm… You fondle them. It’s an amazing feeling… Squish, squish… The sweater feels so thin, it felt as if they were hanging out openly. That doesn’t stop you from taking it off though, sweat dancing off your body as it happens. Resting it on the pile of your scattered clothing, you clasp your hands around the sweaty pillows attached to your chest.

“Ahhhnn~…” Your mouth lets out, heat flowing to your face as you curl up a little. You hug your sides, arms around yourself, squeezing your chest by tightening your arms. “Ahn~!” Another noise pops out of your mouth, your new feelings being simply too much to keep to yourself.

You let them slosh back into place, sweat making them splat together. Feeling for the nipples, you have to pull them upward just to get a good look at them. They’re… inverted. It’s so cute. You force your middle fingers inside them, digging around and getting a good feel for them…

Maybe that’s why she didn’t wear a bra? Cause the nipples wouldn’t stand out, cause they’re not pointy. They always looked so free in her shirt… Now your shirt. You keep one hand firmly wrapped around one of your breasts, rubbing and digging as hard as possible. The other hand, it rests on your thigh… It practically takes itself inside your clit. 

Trying to fit three fingers into it… Your legs clench up, as you start rubbing it more and more. It hurt, but combined with the elation of gripping your tit so roughly, it felt trivial in comparison. “Nnnn~!” You forcefully whine, all the feelings, sounds and smells driving you up the wall as your climax built up, then releasing all over your soft, pretty young fingers. The liquid oozed through the gaps between them, making soft noises as it hit the water. Your body trembles.

That felt… amazing. You stay there, sweaty and breathing heavy, for a few moments. Your hands remain firmly in place, though it’d take so much effort to remove them… Ahh. You’re stuck, taking in the excitement for a little while; But you should really clean up.

Putting on Frisk’s clothing is it’s own stimulating experience, your hand smells distinctly of Frisk’s scent. You ponder internally, if she’s a virgin. You’re actually unsure, but something tells you they must be. You feel calmer now. After washing your hands, you turn on Frisk’s phone.

Ahh! PE is almost over, you should be getting to the roof by now. As you leave the bathroom, you spot someone in the hallway. Squinting to see what that w- Oh. Monster Kid is getting up, after falling flat on his face. Wait, he’s-. He looks back at you, face red. Gosh, did he... hear you?


End file.
